Development of a Novel Hydrostatic Continuously Variable Transmission with Fast Path Switching

Recently, human-robot collaboration is required in many kinds of fields. To develop robotic systems for collaboration with humans, a wide driving range of robotic actuators is necessary. For example, robots for rehabilitation have to conduct some tasks, like supporting human and moving fast. Backdrivability is also necessary for robotic actuators from a viewpoint of safety. A hydraulic closed circuit called an electro-hydrostatic actuator (EHA) is utilized for robotic actuators since they have high power/weight ratio and backdrivability. However, EHA cannot achieve characteristics of both high velocity driving and high force driving since a reduction ratio is constant. This paper proposes a novel hydrostatic continuously variable transmission that has two oil paths with a solenoid valve. The solenoid valve switches between two discrete reduction ratios by switching two oil paths. Furthermore, this paper realizes a continuously variable reduction ratio by switching the two oil paths quickly. This paper confirms that the reduction ratio changes continuously and widely by simulations.